1. Field
The present invention relates to a luminescence device capable of converting an electric energy into light and thereby producing luminescence. More specifically, the present invention relates to an organic electroluminescence device (luminescence device or EL device).
2. Description of the Related Art
An organic electroluminescence device (EL) is attracting as a promising display device because high-luminance luminescence can be obtained with a low voltage. An important characteristic value of this organic electroluminescence device is a power consumption. The power consumption is represented by a product of a voltage and a current, and as the voltage value necessary for obtaining desired brightness is lower and at the same time, as the current value is smaller, the power consumption of the device can be more reduced.
In the manufacturing of an organic electroluminescence device, as for the method to form a thin film that is an organic layer provided between a pair of electrodes, a vapor deposition process such as vacuum deposition and a wet process such as spin coating method, printing method and an inkjet method are being performed.
Among these, when a wet process is used, an organic compound polymer whose deposition is difficult by a dry process such as vapor deposition can be used, and in the case of use for a flexible display or the like, the wet process is suitable in view of durability such as flexibility and film strength and is preferred particularly when fabricating a large-area device.
However, an organic electroluminescence device obtained by the wet process has a problem that the luminous efficiency or device durability is poor.
In recent years, the device efficiency is progressively increased by using a phosphorescent material. As for the phosphorescent material, an iridium complex, a platinum complex and the like are known (see, for example, JP-A-2001-247859 and JP-A-2007-19462), but a device satisfying both high efficiency and high durability has not yet been developed.
Also, an organic EL device where a phosphorescence material substituted with a specific kind of an alkyl group at a specific position with an attempt to obtain a material capable of realizing high efficiency and low voltage of a device is used as a light emitting material has been reported (see, for example, JP-A-2008-210941 and JP-T-2008-505925), but this is insufficient in view of luminescence quantum efficiency, drive voltage, durability and chromaticity shift after device deterioration, and more improvements are being demanded.